08 - Firewire
Firewire is formally known as IEEE1394. It uses two twisted pairs, one for transmit and one for receive, and is a full bi-directional data bus. Firewire also provides power so that a peripheral device can be powered up or have it’s batteries charged. Firewire is common on digital video camcorders. Sony renamed it i.Link, and removed the power pins, which leaves a slightly smaller 4 pin connector.
Firewire has been around a lot longer that HDMI and DVI, and is a lot more mature as far as reliability goes. One big critisim of the interface is that the industry has done a poor job on maintaining compatability between various devices. A new organization, HANA, aims to change that and unite more devices. The current spec of Firewire, 1394b-2002, can carry up to 400Mbit/sec. In addition, there is a CAT5 spec where normal 4 pair CAT5 cable can be used, up to 300 feet, at data rates up to 100Mbit/sec. Firewire is also specified over optical cables. Bridge devices are available that link Firewire using both telcom type single mode fiber, or low cost plastic optical fiber.
Firewire can also be used for data networking. Windows XP, Linux, and Apple’s OS X all have built in support for this, and can be faster alternative to Ethernet for a peer to peer network.
In order to send HD video over Firewire, it must be in a compressed form, such as MPEG2. In a typical implementation, a cable set top box would have a Firewire port, which connects to a Firewire enabled TV. The cable box receives MPEG compressed video from it’s head end, and rather then uncompressing it to convert to analog, or output uncompressed to the HDMI port, it would leave it in it’s MPEG form, and send it out the Firewire port. The TV would then receive the MPEG stream, and using a hardware MPEG decoder, uncompress, and ultimately display the image. However if you don’t already have access to the HD video in some compressed form, only expensive pro grade equipment can re-compress it so that you can put the video onto a Firewire link.
Firewire cables can be made in the field when using 1394b over CAT5. In this case pre-install would be the same as any other CAT5 data cables with RJ45 terminated ends.
A failure of Firewire would appear as all or nothing. Since the data is compressed, data errors due to a damaged cable would result in the loss of the compressed stream, so the audio and video would drop out.